Positioning Methods for Intravascular Electrode Arrays for Neuromodulation

ABSTRACT

A method for positioning an electrode array of a neuromodulation catheter at a target circumferential position along a posterior wall of a superior vena cava includes advancing the catheter to a target longitudinal position within the superior vena cava, and orienting a marker on the extracorporeal portion of the catheter in a circumferential orientation known to position the array at the target circumferential position along the posterior wall. A method of positioning the array at a target longitudinal position includes advancing the catheter into the superior vena cava and using features of the catheter to detect the location of right atrial tissue, such as by sensing for a P-wave using an electrogram captured using an electrode carried at a distal end of the catheter, or by using such electrodes to capture the atrium using atrial pacing pulses. Once the location of the right atria is determined, the electrode array may be deployed in a position known to be proximal to the atrium.

This application claims the benefit of the following U.S. ProvisionalApplications, each of which was filed Nov. 20, 2012 and each of which isincorporated herein by reference: U.S. 61/728,796, U.S. 61/728,799, andU.S. 61/728,805.

TECHNICAL FIELD OF THE INVENTION

The present application generally relates to intravascular electrodearrays for use in neuromodulation. More particularly, the applicationrelates to electrode supports used to position the intravascularelectrodes against the interior wall of a blood vessel and methods usedto position the electrode supports.

BACKGROUND

Prior applications filed by an entity engaged in joint research with theowner of the present application decribe neuromodulation methods usingelectrodes positioned in a blood vessel. The electrodes disposed insidethe blood vessel are energized to stimulate or otherwise modulate nervefibers or other nervous system targets located outside the blood vessel.Those prior applications include U.S. Publication No. 2007/0255379,entitled Intravascular Device for Neuromodulation, U.S. 2010/0023088,entitled System and Method for Transvascularly Stimulating Contents ofthe Carotid Sheath, U.S. application Ser. No. 13/281,399, entitledIntravascular Electrodes and Anchoring Devices for TransvascularStimulation, International Application PCT/US12/35712, entitledNeuromodulation Systems and Methods for Treating Acute Heart FailureSyndromes, and U.S. application Ser. No. 13/547,031 entitled System andMethod for Acute Neuromodulation, filed Jul. 11, 2012 (Attorney Docket:IAC-1260). Each of these applications is attached in the Appendix and isfully incorporated herein by reference. The latter application describesa system which may be used for hemodynamic control in the acute hospitalcare setting, by transvascularly directing therapeutic stimulus toparasympathetic nerves and/or sympathetic cardiac nerves using anelectrode array positioned in the superior vena cava (SVC).

Proper placement of intravascular electrodes is essential forneuromodulation. The electrodes must be positioned to capture the targetnerve fibers, while avoiding collateral stimulation of non-target nervefibers. Mapping procedures are typically performed at the time ofelectrode placement to identify the optimal electrode location. Mappingcan be manually controlled by the clinician or automatically controlledby the neuromodulation system. During mapping, different electrodes,combinations of electrodes, or arrays can be independently energizedwhile the target response to the stimulus is monitored. For stimulationrelating to cardiac or hemodynamic function, parameters such as heartrate, blood pressure, venticular inotropy and/or cardiac output might bemonitored. In some cases mapping includes additional steps ofrepositioning the electrode carrying member so as to allow additionalelectrode sites to be sampled. The mapping process is performed untilthe optimal electrode or combination of electrodes for the desiredtherapy array is identified.

Referenced prior application Ser. No. 13/547,031 describes aneuromodulation system that may be used for hemodynamic control in theacute hospital care setting, by transvascularly directing therapeuticstimulus to parasympathetic nerves and/or sympathetic cardiac nervesusing an electrode array positioned in the SVC. That system includes acontrol system suitable for carrying out the therapy. Theneuromodulation system includes a therapeutic catheter havingtherapeutic elements such as electrode arrays, and optionally, patientand system diagnostic elements; sensors (e.g. pressure sensors, flowsensors, other hemodynamic sensors, other patient condition sensors, andsystem condition sensors such as position sensors, system connectionsensors or other system error condition monitoring sensors). Theneuromodulation system also includes an external stimulator, (alsoreferred to here as a neuromodulator or “NM”). The external stimulatorhas a clinician user interface and functions to provide therapeuticstimulation outputs to the therapeutic catheter; therapeutic outputsthat are dynamically controlled in a closed-loop manner in response toinformation from one or more of the diagnostic elements, or may becontrolled manually by the clinician. The diagnostic elements includesensors for patient hemodynamic feedback such as heart rate (HR), bloodpressure (BP), and other suitable sensed or derived hemodynamicparameters (which may include central venous pressure (CVP), pulmonarycapillary wedge pressure (PCWP), cardiac index, derivations of vascularresistance, cardiac output, and cardiac filling pressures); sensorsand/or analyzers to determine other patient conditions such as cardiacarrhythmia, cardiac capture, respiration, or patient movement; and othersensors and analyzers to monitor system conditions for error,malfunction or unsafe state (referred to as “safety monitoring”) thatshould be indicated to the clinician and/or result in termination ofstimulation.

During use of such systems for hemodynamic control, the electrodes arepositioned at the distal end of an intravascular catheter (referencedhere as the “neurocatheter” or “NC”) percutaneously delivered to thetarget stimulation site within the SVC. The electrodes are placedagainst the SVC wall in order to transvascularly stimulateparasympathetic and sympathetic cardiac nerves. Prior studies haveidentified areas on the posterior wall of the mid-to-cranial SVC,between the brachiocephalic junction and right atrium, where bothparasympathetic and sympathetic nerves can be electrically stimulated.The use of an array of electrodes on the NC allows general placementinto a target region of the SVC without a requirement for preciseplacement. The NC electrode array only needs to be placed into thisgeneral SVC target region to facilitate neuromodulation system function.This region can be defined by both a longitudinal range of the SVC, andby a circumferential range of the SVC (see FIGS. 1A and 1B). Previousdisclosures have identified the preferred longitudinal range as themid-to-cranial SVC, and preferred circumferential range along theposterior side of the SVC.

It is known that accessing the human SVC using the widely accepted,standard percutaneous procedure, especially from venous access sitessuch as the internal jugular, subclavian or femoral veins is a simpleand straightforward technique, in which a variety of clinicians areproficient. In order to provide for both ease-of-use in the acutehospital setting and allow for positioning without the use of imaging,such as fluoroscopy, the NC contains an “array” of electrodes to providea coverage area for capture of target cardiac nerves. All of theelectrodes in the array can then be connected to the NM, and the NM canthen “select” the desired anodes and cathodes by means of electronicswitching circuitry in its response mapping function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top, cross-section view of the superior vena cava (SVC)illustrating a target electrode region for delivery of therapy toparasypathetic and sympathetic targets.

FIG. 1B is an anterior view of the SVC illustrating the target regiondepicted in FIG. 1A.

FIG. 2 schematically illustrates an exemplary neurocatheter positionedwithin the SVC.

FIGS. 3A. 3B, 4A and 4B are plan views illustrating second, third, andfourth embodiments, respectively, of electrode arrays.

FIGS. 5, 6 and 7 are elevation views of first, second and third supportstructures on catheter bodies. The support structures are schematicallyshown disposed within a blood vessel with the portion of the supportstructure that carries the electrode arrays (not shown) biased againstthe wall of the blood vessel.

FIG. 8 illustrates positioning of a support structure in a blood vesselwithin which cardiac rhythm management leads have been previouslypositioned.

DETAILED DESCRIPTION

The present application describes methods that may be used to select adeployment site for the neurocatheter's electrode array within the SVC.Certain disclosed methods include steps selected to ensure that theidentified deployment site places the electrodes where they will capturethe target nerve structures during application of therapy. In theillustrated examples, the target nerve structures are both cardiacsympathetic nerves and parasympathetic nerve targets such as the vagusnerve, but the disclosed methods may be used to select deployment sitesintended to capture one or the other of such nerve targets(parasympathetic or sympathetic). The present application also describesmethods that may be used to select a deployment site within the SVC thatwill place the electrodes a safe distance from the cardiac tissue of theatria, so as to avoid unintended atrial capture during application oftherapy. Finally, methods are disclosed for identifying which electrodesin an electrode array are likely positioned over cardiac rhythmmanagement (CRM) leads also disposed in the SVC, so that alternativeelectrode pairs may be used for the neuromodulation therapy.

NeuroCatheter Positioning During Placement

As described earlier, a preferred method of placement of the NC involvesdeployment of the electrode array into a target region of the SVC, butdoes not necessarily require precise placement. This general targeting,together with the neuromodulation system's automatic mapping responsealgorithm to determine which electrodes within the array produce theoptimal therapeutic response, allows placement of the NC with imagingguidance, typically fluoroscopy, or without any imaging. It isadvantageous to place the NC without fluoroscopy because it minimizesradiation exposure to the patient and clinician, reduces procedure time,cost, and special hospital settings that are required for image-guidedprocedures. Placing the NC correctly without imaging requires the NC bepositioned correctly in the SVC in both the circumferential andlongitudinal directions.

Placing Electrodes at Target Circumferential Position Within SVC

The first method described is for placement of the NC into the targetregion without the use of imaging. More particularly, this method allowsthe electrode array to be positioned in the correct circumferentialposition within the SVC using an electrode array that will not extendthe full circumference of the SVC. This method utilizes a neurocatheterhaving a circumferential marker visible from the exterior of the NC(e.g. a marker on the portion of the neurocatheter shaft that remainsoutside of the body during therapy) that corresponds to the mid-anteriorposition. See, e.g., FIG. 2 which illustrates a neurocatheter 10 havinga marker 2 positioned on the neurocatheter body 4 disposed outside thepatient. By aligning this marker perpendicular to the supine patient,the electrode array in the NC will deploy to cover the preferredcircumferential range on the posterior wall (i.e. the “target region”identified in FIG. 1A). The electrode array and support structure wouldbe manufactured in a fixed orientation with respect to the marker on theNC body. This marker can be a stripe, line or a color coded mark andlabeled accordingly.

Placing Electrodes at Target Longitudinal Position Within SVC

An embodiment for determining correct longitudinal NC placement is byelectrical identification of the position of the right atrium. Aneurocatheter positioned using this technique might be one having a setof orthogonal or ring electrodes, suitable for floating atrial sensingand/or pacing, on its distal end. See, for example, ring electrodes 6 inFIG. 2. In one method that uses atrial sensing, the NC is slowlyinserted while the neuromodulator displays the sensed electrogramsignal. The clinician advances the NC until atrial intracardiacelectrical activity (P-waves) is displayed. Once P-waves are displayed,it is known that the NC distal tip is just inside the right atrium (RA).At this point, the NC is pulled back a fixed distance (preferably 1.5cm) from 1 to 4 cm into the SVC by using graduated markings on the NCbody or by handle design. Once pulled back, the electrode array can bedeployed (into the position shown in FIG. 2) and will be in the correctlongitudinal region.

In another method, atrial pacing is used to identify the location of theright atrium. As the NC is advanced, the clinician enables one or aseries of pacing pulses above typical atrial capture thresholdssynchronized to the patient's cardiac rhythm (as detected from theneuromodulation system's ECG detection function previously disclosed).The clinician advances the NC until atrial capture is detected,indicating the right atrium has been reached. In one preferredembodiment, the neuromodulator automatically determines atrial captureby signal processing looking for the evoked response as a result of thepacing pulse. In another embodiment, the clinician detects atrialcapture from the displayed ECG. In either case, the identification ofthe location of the right atrium is used as previously described toidentify longitudinal position, where the NC is pulled back as describedpreviously and the NC electrode array deployed.

Another preferred embodiment uses an inner lead extendable from theneurocatheter. This lead includes a set of orthogonal or ring electrodessuitable for floating atrial sensing and/or pacing. For example, thelead supporting electrodes 6 shown in FIG. 2 would be extendable asdescribed in this paragraph. Once the NC has been inserted into the SVC,the clinician fully extends the atrial “floating lead” from the NC usinga handle at the proximal end of the NC. The floating lead, when fullyextended, represents a known, appropriate distance (preferably 1.5 cm)from the distal edge of the deployed NC electrode array. Using theatrial sensing method as described above, the NC is slowly insertedwhile the NM displays the sensed electrogram signal. Once P-waves aredisplayed, the distance from the right atrium to the distal edge of theNC electrode array, once deployed, is known. At this point, theelectrode array can be deployed and will be in the correct longitudinalregion. Alternatively, the atrial pacing method described above can beused with this embodiment. More specifically, as the NC is advanced withits extended “floating lead”, the clinician enables one or a series ofpacing pulses as described earlier. The clinician advances the NC untilatrial capture is detected, indicating the right atrium has beenreached. In either case, the identification of the location of the rightatrium is used as previously described to identify longitudinal positionand safely deploy the NC electrode array.

Another preferred embodiment to facilitate longitudinal placement is bymeasured distance from the venous access site to the mid-to-cranial SVCand use of graded markers, similar to a ruler, on the shaft of theneurocatheter. A relative measurement device (similar to a tape measure)is used to “measure” the distance from the entry site (jugular,subclavian, or femoral vein) to an anatomic mark on the surface of thepatient's chest. Then the NC is introduced and inserted until thecorresponding marker on the NC body is aligned with the introducersheath entry site. For example, the typical distance from the jugular orsubclavian vein entry site to the right atrial-SVC junction is 16.5 cm.The tape measure could be used to measure from the entry site to ananatomic landmark, such as the sternum. A relative marker thatcorresponds to 1-2 cm short of the right atrium (equivalent to a NCdepth of 14.5 to 15.5 cm) is used to determine the proper insertiondepth for the clinician.

In addition to the above-described methods, if desired, the NC can beplaced in the correct circumferential and longitudinal orientation is byusing fluoroscopic imaging. The NC will have radiopaque materials onboth the NC body to facilitate longitudinal positioning prior toelectrode array deployment, as well as on the electrode array and/ormechanical support structure. These markers can be used to assurecorrect position in the SVC target region by aligning the markers withanatomic landmarks such as the brachiocephalic junction or the rightatrium.

Preventing Unintended Stimulation of Cardiac Tissue

An additional feature of the neuromodulation system is one that ensuresthat the therapeutic neurostimulation does not result in unintendedcapture of cardiac tissue, that is, capture of right atrial tissue as itmeets the SVC. The primary method to prevent unintended capture ofcardiac tissue is through proper positioning of the NC as describedearlier. Only an incorrectly positioned NC can result in an electrodearray that is deployed in contact with atrial tissue. However, an addedsafety feature in the event that the NC is positioned too close to theright atrium or migrates after placement will next be described as ameans to prevent inadvertent atrial capture. In particular, a singletest stimulus or series of stimuli prior to initiation of therapeuticneurostimulation to look for inadvertent atrial capture. The teststimuli will be applied using each of the electrode pairs (“test pairs”)in the array that are closest to the right atrium. The test stimuli aredelivered at high output energy, and synchronous to the ECG in order toassure they are delivered outside of the atrial refractory period. Thismethod can be utilized with any electrode array geometry including thoseshown in FIGS. 3A through 4B, however an electrode array geometry suchas the type shown in FIG. 4A may be particularly useful for this methodgiven its use of additional circumferential distal electrodes, closestto the right atrium. This array provides preferential circumferentialcoverage to test for inadvertent atrial capture, and may enhance thissafety feature.

During delivery of the atrial test stimuli, the clinician monitors theECG recorded by the neuromodulation system. The physician verifies thatthere is no capture of atrial tissue as a result of the test stimulus.Once verified, the clinician indicates that the neuromodulator canswitch to the next “test pair” in the array and repeats the process, oralternatively, the NM can automatically switch to each of the testpairs. Once all pairs have been evaluated for inadvertent atrialcapture, the clinician can then safely begin neurostimulation.

In another preferred embodiment, the NC contains a “floating lead”(described earlier) that extends into the right atrium. In this case,the atrial evoked response can be detected automatically by the NM. TheNM will sequence through each of the electrode array “test pairs”, andenable the start of therapeutic neurostimulation only if no evokedresponse is detected as each of the “test pairs” are evaluated.

NeuroCatheter Positioning in the Presence of Existing CRM Leads

In some cases the neurocatheter may be used in patients havingpermanently implanted CRM devices and the chronic leads that are usedwith such devices. Such CRM leads typically run from the transvenousentry site of the subclavian vein through the SVC towards the heart. Asa result, some patients will have leads existent in the SVC when the NCis deployed. Also, it is conceivable that one or more lead bodies willlie in the target region for parasympathetic and sympathetic nervecapture. The CRM lead bodies, which are covered with silicone orpolyurethane insulation, may be free floating in the vessel or attachedto the vessel wall and covered with fibrotic or scar tissue (eitherpartially or fully covered), as shown in FIG. 8. Also, in the case ofdefibrillators and cardiac resynchronization therapy defibrillators, aconductive defibrillation coil electrode may be existent, also shown inFIG. 8. As a result, the NC's electrodes may encounter lead insulation,scar tissue or fibrosis, or the conductive defibrillation coil.

Features of the disclosed electrode array allow target nerve capturedespite the presence of CRM leads.

In circumstances where the electrode array will be deployed on top ofexisting CRM lead bodies or a defibrillation coil electrode, the arrayof electrodes in combination with the neuromodulation system'spreviously disclosed automatic response mapping function can allowtarget nerve capture despite the presence of the CRM lead. Thisneuromodulation system mapping function can determine the preciseelectrodes in the array required for capture of the desiredparasympathetic and sympathetic cardiac nerves by an algorithm run bythe neuromodulator. After placement of the NC in the target SVC region,the neuromodulator initiates stimulation using an electrode pair andlooks for HR and BP response, continues to the next pair looking forresponse gain, and so forth. Early preclinical and clinical data hasshown that more than one electrode pair can capture the target nerves.Therefore, in the event that CRM lead insulation, fibrosis, or adefibrillation coil electrode impact the ability to capture with oneelectrode pair, adjacent pairs in all directions provide added optionsfor target nerve response.

Also, during the automatic response mapping function, the impedancebetween electrode pairs is measured during each mapping step to avoidpairs that have very high impedance (which would indicate the pair isdeployed in the presence of lead insulation) or pairs that have very lowimpedance (which would indicate the pair is deployed in the presence ofa conductive defibrillation coil electrode). This impedance checkingstep ensures that the automatic response mapping algorithm only testselectrode pairs that have the potential for target nerve capture, andquickly eliminates pairs that may be deployed in the presence of CRMleads.

Exemplary Electrodes

Additional details of the electrode arrays shown in FIGS. 3A-4B willnext be described. In general, the electrode arrays and their associatedsupports may be elements of a catheter that includes a catheter body,the support structure on a distal portion of the catheter body, and theelectrode array on the support structure. As disclosed in the priorapplications referenced herein, electrodes in the electrode array areelectrically coupled to a neurostimulator that energizes the electrodesusing stimulation parameters selected to capture the target nerve fibersand to achieve the desired patient effect.

In a preferred arrangement, the electrode array includes a flexiblesubstrate. The substrate is preferably formed of an insulating material,such as a polymer (including silicone, polyurethanes, polyimide, andcopolymers) or a plastic. Thus electrode surfaces will be exposed on oneside of the array (the side intended to be against the SVC wall) andinsulated by the substrate on the other side of the array in order tocapture target nerves through the SVC wall with efficient stimulationenergies, and avoid collateral stimulation through the blood pool. Wherethe neurocatheter is to be used for acute use (typically 36-72 hours,but in general less than 7 days), the electrodes may be constructed of avariety of alloys, including stainless steel, titanium, cobalt chromium,and platinum alloys.

The electrodes are arranged on the substrate in a variety of geometriesin order to provide the desired stimulation “coverage region” (bothcircumferentially and longitudinally). FIG. 2 shows a preferredelectrode array on substrate 8. The array is arranged in a rectangularshape that contains a 4×4 array of electrodes 14 for a total of 16electrodes. The drawing shows what would be the posterior face of theelectrode array within the SVC (i.e. the face that contacts theposterior region of the wall of the SVC lumen). In this arrangement, thesubstrate has a geometry resembling a fork—with a plurality of parallel,longitudinally extending tines or fingers 16 laterally separated fromone another at their distal ends. Linear arrangements of electrodes aredisposed on each such finger 16. Other preferred embodiments includeother geometric arrays that contain from 4 to 32 electrodes, and thatcan be arranged in, or on substrates having, rectangular, circular (FIG.3), oval (FIG. 4B) or irregular configurations, such as the one shown inFIG. 4A. As shown, these embodiments can likewise includelongitudinally-extending fingers 16 with linear arrangements ofelectrodes disposed on them. These can be arranged to provide aneffective coverage area that spans greater circumferential area asdepicted in FIG. 4A, or greater longitudinal area, as depicted in FIG.4B.

Independent of geometric shape, each electrode in the array will bespaced from adjacent electrodes by a longitudinal distance, d_(L), and acircumferential distance, d_(c). The spacing between electrodes ischosen to optimize capture of target nerves, and may be from 1 to 10 mm,typically 5 mm, and the longitudinal and circumferential spacing may beequal or may differ.

In some embodiments, the array might include a greater circumferentialexpanse of electrodes in the distal electrodes (see, e.g. FIG. 4A),which in use are positioned closest to the right atrium. Where theneurocatheter is introduced using a femoral approach, the most proximalelectrodes in the array will lie closest to the atrium and might beprovided with a greater circumferential expanse. This arrangement canfacilitate positioning methodologies that allow safe positioning of thearray so as to avoid the risk of atrial capture, as disclosed above.

The electrodes can be constructed on the substrate using a variety ofmanufacturing techniques, including subtractive manufacturing processes(such as mechanical removal by machining or laser cutting), additiveprocesses (such as laser sintering, deposition processes, conductorovermolding), or combinations (such as printed circuit technology withadditive plating). When assembled on the catheter, the electrodes andsubstrate (where used) will be attached to or manufactured on amechanical support structure (described below) having features forbiasing the electrodes against the vascular wall and, optionally,supporting the distal end of the neurocatheter against the vascular wallor spaced from the vascular wall.

Mechanical Support Structure for the Electrode Array

In order to capture target nerves through the SVC wall with efficientstimulation energies, secure engagement of the electrodes against theSVC wall is desired. Therefore, the catheter includes a supportstructure or structures that provide mechanical force to press theelectrode surfaces against the SVC wall once deployed. Additionally, thesupport structure securely but reversibly (at least in the case of anacute device) anchors the catheter to prevent its migration within thevasculature. The support structures are constructed of a variety ofshape memory alloys, such as nickel-titanium, or other alloys that wouldbe mechanically positioned by mechanisms in the catheter body. Where thesubstrate described above is used to form the array, the supportstructures may be integral with the substrate, or coupled to thesubstrate.

Preferred embodiments for the support structures include a fullcylindrical configuration, shown in FIG. 5, a fork configuration, shownin FIG. 6, and a partial cylindrical configuration, shown in FIG. 7. Inall of these configurations, the electrode array, which is only requiredto cover a portion of the circumference of the SVC, will be attached tothe support structure. In FIGS. 5 through 7, the electrode array is notshown to allow the support structure to be more easily seen. Inpreferred embodiments, the electrode arrays with the associatedinsulative substrates disclosed above are used.

In use, the support structure is radially expanded at the targetelectrode site within the vasculature using known means. For example,the support structure with the attached electrode array may becompressed within a deployment sheath for advancement through thevasculature, and then released from the deployment sheath at the targetelectrode site. The support structure self expands at the target site,or is actively expanded using a balloon or other expansion structure,positioning and biasing the electrodes against the vessel wall.

The full cylindrical support structure 12 a (FIG. 5) includes acylindrical portion 17 formed of a plurality of parallellongitudinally-extending support elements 18. When the support structureis expanded within the vasculature, the support elements of thecylindrical portion contact the vessel wall. The electrode array iscarried on the cylindrical portion of the support structure, and inparticular is mounted to a subset of the longitudinally-extendingsupport elements that expands towards the target SVC wall region. Forexample, each of the longitudinal fingers 8 of the substrate shown inFIG. 2 may extend along four adjacent longitudinally-extending elements18 of the cylindrical part of the support structure. The opposedlongitudinally-extending support elements forming the cylindricalportion contact the opposed portion of the vessel wall, such that theentire array of longitudinal support elements aid in securing theelectrode array to the vessel wall.

In the FIG. 5 arrangement, the support structure biases the distal endof the neurocatheter's body 30 towards the center of the SVC lumen asshown. This central positioning of the neurocatheter body 30 anddeployed structure for the electrode array creates a uniform shape thatresults in central, more uniform laminar blood flow patterns to preventthrombosis. In this central design, adequate space does exist throughopenings in the support structure on either side of the catheter body toallow other catheters or devices to be inserted through the SVC whenneeded. The FIG. 5 embodiment includes cross members 20 to providecircumferential structure. These cross members are positioned at thedistal and, optionally, proximal ends of the support structure betweenstruts 21 that angle inwardly from the longitudinally-extending members.This places the cross members struts away from the vessel wall when thestructure is fully deployed as shown in FIG. 5, rather than between thelongitudinally-extending members of the cylindrical portion, thusleaving the spaces between the longitudinally-extending members 18 (andthus the spaces between the longitudinal columns of electrodes on thosemembers) clear. Where the electrodes are being deployed in an area ofthe SVC where cardiac rhythm management (CRM) leads reside, these spacesgive room for the columns of electrodes on the neurocatheter tocircumferentially shift around existing lead bodies and into contactwith an adjacent portion of the vessel wall, as will be discussed infurther detail in connection with FIG. 8.

Another embodiment of a support structure is the fork support structure12 b shown in FIG. 6. This embodiment includes a series of longitudinalmembers 22. These members have distal sections 24 running in parallel toone another and including free distal ends 26, similar to tines of afork. Proximal sections 28 extend from the neurocatheter body 30 to theproximal ends of the distal sections 24. The electrodes are positionedalong the distal sections (with or without the substrate arrangementsdescribed above). When released from a deployment sheath, the forkstructure expands to position each of the distal sections 24 and theirassociated electrodes against the SVC wall. This arrangement minimizesmaterial and facilitates better compression into the deployment sheathto minimize delivery diameter. By applying mechanical forces on one sideof the wall (in contrast with the forces applied around the cylinder inthe FIG. 5 embodiment), the distal portion of the neurocatheter body 30is biased towards the portion of the SVC wall opposite to the portionagainst which the electrodes are biased, as shown in FIG. 6. This leavesmaximum cross-sectional space between the longitudinal members, allowingother catheters or devices to be inserted through the SVC, as would betypically required for patients in acute hospital care. In addition, byhaving the neurocatheter body positioned against the vessel wall,central blood flow disruption can be minimized to prevent thrombosis.Also, like the full cylindrical structure and as discussed further inconnection with FIG. 8, the individual longitudinal members 22 leavespace between the longitudinal columns of electrodes so that if, uponexpansion of the support structure, the longitudinal columns collidewith resident CRM leads within the SVC, the columns can shift intocontact with SVC wall space adjacent to the CRM leads.

The support structure 12 c of the FIG. 7 embodiment combines features ofthe FIGS. 5 and 6 embodiments by combining a partially cylindricalstructure with opposing mechanical support legs 22 a (e.g. two or morelegs of the type used in the FIG. 6 embodiment). In this configuration,a partial cylinder 17 a of support elements 18 a carrying the electrodearray is secured against the SVC wall on one side of the deployedsupport structure, and a number of opposing elements or legs 22 aexpands on the other side of the support structure to provide an equaland counteracting force against the SVC wall opposite the target region.The partial cylindrical structure may incorporate features of the FIG. 5support structure, but will extend less than 360 degrees around thecircumference of the SVC. The number of opposing legs 22 a wouldpreferably be 2, but more legs, up to 6, can be included. In thisarrangement the distal portion of the neurocatheter body 30 is againbiased towards the center of the SVC, as in the full cylindricalconfiguration. In a variation of this embodiment, the support legs 22 ashown in FIG. 7 may be positioned against the blood vessel wall on oneside of the blood vessel, and the members 24 of the fork-like structureof the FIG. 6 embodiment (with the electrode array thereon) positionedon the opposed portion of the blood vessel wall.

Electrode Array Use in the Presence of Existing CRM Leads

As noted above in connection with FIG. 8, in some cases theneurocatheter may be used in patients having permanently implanted CRMdevices and the chronic leads that are used with such devices. Themechanical layout and design can array allow target nerve capturedespite the presence of CRM leads. In particular, the mechanical layoutand design of the neurocatheter electrode array and support structurefacilitate engagement in the presence of CRM lead bodies. A critical andcommon feature of both the fork and cylinder support structures is thatthey have parallel elements with openings where engaged to the targetSVC vessel wall. These openings provide the most flexibility whenengaging against the vessel wall in the presence of chronic CRM leads,by allowing the electrodes to engage against irregular surfacespresented by attached lead bodies and the ability to have thelongitudinal electrodes engage the SVC wall by moving between or aroundfree floating leads to engage active tissue.

It should be recognized that a number of variations of theabove-identified embodiments will be obvious to one of ordinary skill inthe art in view of the foregoing description. Moreover, it iscontemplated that aspects of the various disclosed embodiments may becombined to produce further embodiments. Accordingly, the invention isnot to be limited by those specific embodiments and methods of thepresent invention shown and described herein. Rather, the scope of theinvention is to be defined by the following claims and theirequivalents.

All prior patents and applications referred to herein, including forpurposes of priority, are incorporated by reference for all purposes.

I claim:
 1. A method for positioning an electrode array of a neuromodulation catheter at a target circumferential position along a posterior wall of a superior vena cava, the method comprising: providing a neuromodulation catheter including a catheter body, an electrode array on a distal portion the catheter body, and a marker on the catheter body, the marker positioned to face a mid-anterior position when the electrode array is at the target circumferential position along the posterior wall; advancing the catheter to a target longitudinal position within the superior vena cava, marker remaining outside the body; with the patient in a supine position, orienting the marker perpendicular to the patient.
 2. A method for selecting a longitudinal position for an electrode array within a superior vena cava for delivering therapeutic stimulus transvascularly to parasympathetic and/or parasympathetic nerve fibers, comprising; positioning a catheter having the electrode array thereon within a superior vena cava; sensing an electrogram using an electrode at the distal end of the neuromodulation catheter and; advancing the catheter within the superior vena cava while observing the sensed electrogram; upon observing a P-wave on the sensed electrogram, proximally withdrawing the catheter by a distance of between 1 and 4 cm and then anchoring the electrode array within the SVC. 